Vacuum oven



Thomas Griff/#7. 1

Patented June 2, 1925.

UNITED STATES 1,540,401 PATENT OFFICE.

MERVIN J. KELLY, OF NEW YORK, N. Y., AND THOMAS R. GRIFFITH, OF DOVER, NEW JERSEY, ASSIGNORS TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORFORATION .OF NEW YORK.

VACUUM OVEN.

Application led August 24, 1920. Serial No.,405,768.

To all 'whom t may concern Be it known that we, MERVIN J. KELLY and THOMAS R. GRIFFITH, citizens ofthe United States, residing at New York, in the county of New York, State of New York,

` and at Dover, in the county of Morris, State of New Jersey, respectively, have invented certain new and useful ln'iprovements in Vacuum Ovens, of which the following is a full, clear, concise, and exactdescription.

rrlhis invention relatesto ovens, and has particular reference to electrically heated ovens, suitable for heating metallic parts, such as the electrodes of vacuum tubes.

An object of the invention is to concentrate on the charge within the oven the heat u which is generated for heating the oven.

The oven comprises a water-jacketed vessel which is adapted to be connected to a vacuum pump for removing gas evolved by the charge and which contains a hollow7 tube serving as the oven wall and around which is positioned an electrically heated wire. To effect the desired concentration of the heat, around the'oven wall are arranged a pluralityof heatreflecting surfaces to concentrate the heat at the centre of the oven, and other reflectors are employed within the oven to concentrate the heat on the charge. This reduces to a minimum the loss of heat by reflection and loss by conduction is minimized by the evacuated space'surrounding l the oven.

The invention is illustrated in the figure,

which represents a central longitudinal sectionwof the device with some few parts being shown in elevation.

As shown in the figure, the invention comprises an outer clinder 1 which may be made of any suita le material such assheet brass. Thevbottom of cylinder 1 is closed by a circular metallic plate 2 of metal, such as brass, which is soldered to the cylinder 1. This circular plate 2 isprovided along its upper edge with a fiange portion 3, having an interior shoulder 4 in which another vessel, to be later described is seated. The flange 3 at intervals throughout its circumference is provided with cut-away portions 5 which extend down to the plate 2. As will be apparent hereinafter, these cut-away portions 5 provide means whereby cooling fiuid may circulate around. the oven. The plate 2 is provided with an aperture G into which a metallic nipple 7, preferably of brass, 1s inserted and to which nipple at its outer end a pipe -or hose 8 is attached for the purpose of introducing a cooling medium around the oven. To the upper end of the cylinder 1 there 1s fastened a metallic ring 9 by any suitable means such as screws 10. This ring may he of any suitable material such as brass. In the lower face of the ring 9 is a circular groove 11. Into this groove the upper end of a cylindrical container12 is fitted. The joint between the container 12 and ring 9 is soldered so that it is air tight. The cylindrical container 12 is made of a Asuitable metal such as brass and preferably of seamless brass tubing so that it is as air tight as possible. The bottom of container 12 is closed by means of ay plate 13, also, preferably of brass, and having an upturned peripheral edgelll which embraces the lower end of the container 12 and is soldered thereto. The plate 13 rests in the shoulder 4 of the flange 3 ofthe plate 2,\"previ'ously mentioned, and by this means the container 12 is Yfirmly and positively seated within the cylindrical receptacle 1 and is suitablv spaced therefrom. u

Near the lower end of the container 12 there is provided an aperture. In line with this aperture on the outside of container 12, there is positioned a plug 15 having an inner bore which registers with the above mentioned aperture. This plug has a flanged portion thereon which is riveted to the .container 12. The 'plug 15 extends from the outer face of the container 12 to the inner face of the cylindrical receptacle l. The apertures in container 12 and the inner bore of plug 15 are threaded to receive a similarly threaded portion ofa nipple 16. This nipple 16 is adapted to receive a pipe or hose 17 and has a flange portion 18 thereon, so that as it is threaded into the plug 15, the fiange portion 18 bears against the outer face of the cylindrical vessel 1v and grips the same between itself and the plug l5 to make a tight joint. Solder may also preferably be applied to these joints to make them tight.

A cap 19 is adapted to be attached to the upper portion of ring 9 by suitable means such as screws 20. A filling 21 of wax or other material may be placed between these two faces to make their union tight. The cap 19 is preferably made of brass and has a flange 22 which has an annular groove 23 in its upper face, in which any suitable material such as wax, heavy oil or grease may be placed. The flange portion 22, which is apertured, is adapted to receive a plate of insulating material 24 which rests on the top of the flange portion 22 and bears against the groove 23 containing the packing material. This insulating portion may be of any suitable material but is preferably made of a glass such as pyrex lieat-resisting glass. This plate 24 is provided with apertures through which extend hollow exter` nally threaded brushings 26, the upper ends of which are adapted to be engaged by the nuts 27. Between the enlarged ends of the bushings 26 on one side and the nuts 27 on the other side of the glass plate, lead washers 28 are positioned. Through the hollow portion of the bushings 26 extend terminal rods 29 preferably of copper and which when correctly positioned are soldered to the bushings 26. These rods 29 are provided with binding posts 30 to which electrical terminal wires 31 may be attached. The lower ends of the rod 29 are slotted to receive a pair of terminal springs 32; which are riveted thereto.

At intervals around its periphery, the ring 9 is provided with cut-away portions 33 to provide passage for the circulating medium in the space between receptacle 1 and container 12. The upper end of receptacle 1 extends somewhat beyond the level of cap 19 and at one side is provided with an opening 34 adjacent which is riveted a receptacle 35 having an aperture 36 in its bottom to which a nipple 37 is attached for the passage of cooling medium from the receptacle 35 through a pipe or hose 38.

The lower face of cap 19 is provided with an inner shoulder 39 against which bears the upper end of a hollow cylinder 40. This cylinder 40 is preferably made of refractory insulating material such as alundum which is porous, and which extends from the shoulder 39 downwardly to the bottom of container 12 upon which it rests. By engaging with the shoulder 39, the hollow cylinder 40 is positively positioned within the container 12. Around a certain ortion of the cylinder 40 on the exterior sur ace thereof, is wound a plurality of turns of electrical heater wire 41, preferably of molybdenum. The lower end of this wire passes upwardly through a tube of insulating material 42 preferably of quartz glass and is attached at its upper end to a binding post 43, a portion of which passes through the refractory cylinder 40 and connects with a copper contact plate 44. Similarly, the other end of the heater-wire 41 passes through a tube 45 and connects to a binding post 46 which in turn makes connection with a copper contact plate 4T. In the process of winding this heater-wire on the refractory cylinder 40, it is generally customary to place a coating of some heat cement thereover to effectively cover the wire and maintain it in proper position. This cement is not shown in the drawing. When the plate 24 is placed in position on the flange portion 22 of the cap 19, it is turned until the terminal contact springs 32 make contact with the copper contact plates 44 and 47 whereby Vthe electrical circuit through the oven is closed.

Surrounding the refractory cylinder 40 are a plurality of cylindrical surfaces 48, 49 and 50 which are made of any suitable material but preferably of highly polished nickel. These surfaces are spaced throughout their length but are lapwelded together at their ends. The upper ends of these surfaces bear against the inner shoulder 51 of the ring 9 and are thereby suitably positioned within the container 12. The lower ends of the surfaces 48, 49 and 50 are welded to a flanged portion 52 which beai's against the outer lower end of the refractory cylinder 40 which therefore tends to maintain the proper space relation between the refractory cylinder and the highly polished surfaces.

The space within the refractory cylinder 40 is adapted to receive the charge to be heated in the oven. In the bottom of the space is placed a plurality of highly polished metal plates 53, 54 and 55 which may also be of nickel. These plates 53, 54 and 55 are spaced apart a suitable distance by annular nickel rings 56 and are held in this space relation by wires 57 which are passed through apertures in the various plates and around the nickel rings 56. The lower portion of these wires 57 are twisted together and rest on the bottom of container 12 to space the lowermost plate from the bottom of the container. When the charge is placed within the refractory cylinder 40, a plurality of reflecting plates is placed on top of the charge and shown in the drawing at 58. This upper plurality of polished metal surfaces are provided with handle portions 59 whereby they can readily be removed.

The receptacle 1 may be supported on any suitable platform such as 60 and is supported thereon by being pinned or riveted to an annular flange 61 which in turn is conncted to the platform 60 by means of screws 6 In the operation of the device` the oven is assembled as shown in the figure, with the. charge loaded in the refractory cylinder 40 between the upper and lower Sets of polished metallic surfaces. In one preferred operation of the oven, this charge comprises the metal plates and grid surfaces and some until terminal springs 32 make contact with the plates 44 and 47. f

As it is necessary in this particular op eration of the oven to attain temperatures in the neighborhood of 1100 degrees C., for the proper glowing and treatment of the material above, mentioned, it is necessary to properly concentrate the heat within the oven in that portion yin which the charge is placed so as most efficiently to use the heat and for that purpose the polished nickel- Surfaces 48, 49 and 50 are provided as well as the polished surfaces above mentioned which are placed within the refractory cylinder above and below the charge. Ilias much as these high temperaturesare often attained inthe ordinary use of this oven, it is furthermore necessary to provide a simple and efficient method of circulating a cooling medium in the spaces between the receptacle 1 and the inner container 12. For this purpose a suitable cooling medium such as water is passed through the pipe 8 into the lower space between the bottom of receptacle 12 and lower cap 2vand up4 between the openings 5 of the flange 3 of the cap 2 and then around the side of the container 12 in the space between it and the receptacle 1. The circulating medium then passes through the out-away portions 33 in the upper ring 9 and flows around the `top of cap 19 and the flange portion 22 thereof and out through the opening 34 in the side of the upper portion of receptacle 1 into receptacle 35. Thence it passes through the nipple 37 and out through the hose or pipe 39. Y l

Furthermore, in the uses to which this oven may be applied, it is desirable, particularly in treating the electrode metallic portions of thermionic discharge devices, thatwhen the gases and vapors contained within the same are driven off by the heat, these gases and vapors can simply and readily be removed from the heat center. For this purpose the opening of the lower portion of receptaclel 12 is connected with the plug 15 and nipple 18 and the hose of pipe 17 so that this pipe or hose may be connected to a suitable vacuum system. Passages are provided in ring 9 to permit the ready withdrawal of gases evolved from the charge and passing through the porous oven wall 40.

Furthermore, in view of the high temperatures ordinarily attainable in the use of this oven, it is necessary not only that the heat for the treatment of the charge be concentrated on the charge itself, which is effected by means of the above means reflecting surfaces, but that the reflecting surfaces them.

selves be within the container 12 so that there will be removed from the reflecting surfaces all the gas and vapor they may contain and which they might otherwise give up to the material to be treated. At the same time it is necessary to keep these parts just as cool as possible so that they shall not 4lose their highly polished condition due to the intense heat and therefore be unable to reflect the heat properly. The vacuum which is maintained in the container 12 is also an important factor in preventing the oxidation of the polished surfaces.v

Vhile I have described the parts of this oven as being comprised of certain materials it is to be clearly understood that these are cited merely for the purpose of showing one preferred form in which this o-ven may be made. chanical structure are obviously possible without involving a departure from the spirit of the invention.

that is claimed is:

1. An electric oven having an air tight chamber, a heating member within said chamber adapted to receive a charge to be heated, a plurality of highly polished metallic plates surrounding the charge to con- L fine the heat to the vicinity of the charge.

,2. An electric oven having an air tight Other modifications of the mechamber, a closure for one end of said chamber, a heating cylinder within said chamber, a shoulder on said closure engaging with one end of said cylinder to position the same within the chamber.

3. An electric oven having an air tight chamber, a closure for one end of the chamber, a heating member within said chamber, a heat retaining screen around said heating member, means at said closure engaging with the one end of the heating member and the heat retaining screen to position the heating member and screen within the chamber.

4. An electric oven comprising a refractory heating member enclosing a heating space, a screen surrounding said heater in close proximity thereto, said screen comprising a plurality of highly polished spaced metallic walls.

5. An electric oven having an air tight chamber, a refractory heater within said cl1amber,"-said heater enclosing a heating space, a screen surrounding said heater in close proximity thereto, said screen comprising a plurality of highly polished spaced metallic walls, electric current terminals for said heater. a vessel surrounding the air tight chamber and means for introducing a cooling medium between said vessel and said chamber.

6. An electric oven having a cylindrical air tight chamber, a cap closure for one end of said chamber, shoulders on said cap closure, a cylindrical heating member and a cylindrical screen around said heating member and within said chamber, one end of said heating member and cylindrical screen engaging With said shoulders, means for maintaining a vacuum in said chamber, an

outer vessel around said chamber and means for maintaining a circulation of cooling medium between the outer vessel and said chamber.

7. An electric ovenhaving an air tight chamber, a closure for one end of said chamber, an opening in said closure, a heating member Within said chamber having circuit closing contacts thereon, a plate for closing the opening in said closure, electric terminals carried by said plate, said terminals` a plurality of high polished spaced metalv plates, said unit adapted to support the charge to be heated Within the heating member and a second reflecting unit similar to the first mentioned unit and adapted to be placed above the charge when the same has been inserted Within the heating member.

10. vAn oven comprising a heating chamber, a heat reflecting member in said chamber for supporting the charge, and a second heat reflecting member :tor covering the charge.

11. An oven comprising a heating chamber, a heat reflecting member in said chamber for supporting the charge, and .a second -heat relecting member for covering Vthe charge, each of said heat reflecting members comprising a plurality of polished surfaces.

12. In an oven, a cylindrical heating chamber, and a plurality of heat reflecting screensloosely itting in said chamber.

13. In combination, a heating chamber, a polished heat reflecting member, and means for applying a cooling medium adjacent said member for protection of the reflecting surfaces.

14. In an oven, a charge receiving chamber comprising a Wall of refractory insulating material, a heaterY of resistance Wire Wound on said Wall, contact terminals for said heater extending through said Wall, and cooperating contacts insertible in said chamber for connection to an external circuit.

In Witness whereof, We hereunto subscribe our names this 17th day of August A. D., 1920.

MERVIN J. KELLY. THOMAS R. GRIFFITH. 

